1. Field of the Invention
The present invention relates to an organic electroluminescent panel and a producing method thereof.
2. Description of the Related Art
In an organic electroluminescent (hereinafter, referred to as “EL”) panel, a surface-emitting element due to luminescent areas of an organic EL element is formed on a substrate. A single or plural surface emitting elements are arranged to form a display region. A lower electrode having one of various structures is formed on a substrate. A film pattern of organic layers including an organic electroluminescent layer is then formed, and an upper electrode is formed on the film pattern. When the film pattern is formed, a film forming mask which has openings corresponding to the pattern shape is used, and a desired pattern is formed by a film forming method such as the mask vapor deposition method.
The pattern formation of the organic layers by using a film forming mask will be described. Usually, luminescent areas of an organic EL element are defined by an insulating film formed on a substrate. A film pattern of organic layers is formed on the luminescent areas by using a film forming mask having an opening which is slightly larger in size than the luminescent areas. In the case of plural-color display, film forming masks respectively having openings corresponding to electroluminescent color patterns are used. The masks are adequately replaced with one another or slid so that organic electroluminescent layers of different colors are formed (See JP-A-2002-367787).
The organic layer refers to layer having an organic electroluminescent layer constituting organic EL (such as an emission layer, a hole-transport layer, an electron-transport layer, a hole-injection layer, and an electron-injection layer) which include an organic electroluminescent layer, and which are to be stacked above and below the organic electroluminescent layer. An organic EL element is not restricted to have plural organic layers, and may consist of a single layer, or only an organic electroluminescent layer. For a hole-transport layer and an electron-transport layer which are usually made of a single material on the same substrate, film forming masks having different patterns for respective electroluminescent colors are often used in order to control the film thickness in respective electroluminescent color regions (See JP-A-2001-237068).
In the case of a single-color display, a film forming mask having a predetermined pattern (for example, a stripe shape) corresponding to a luminescent areas is used. In order to avoid the strength of the mask from being reduced by excessive density of openings, a film pattern of organic layers is formed in a display region while the formation pitch of the openings is enlarged, and plural film formation steps are conducted (See JP-A-2000-48954).
The pattern formation using the film forming mask is often employed not only in the above-described pattern formation of the organic layers, but also in pattern formation of other components of an organic EL element, such as upper and lower electrodes, an insulating film, and a sealing film.
Hereinafter, a film formation region refers to a region which forms each organic EL element in accordance with an opening of the film forming mask. The film formation region is set by a design of the openings of the film forming mask. The film formation region is set by, for example, the width or length of the opening or the position of the opening in the film forming mask.
In case where the film forming mask is used for producing the pattern formation of components such as organic layers, electrodes, an insulating film, and a sealing film, a film forming material, dust, or the like (attachment substance a) sometimes adheres to an opening 1A of a film forming mask 1. (Please see FIG. 1A) Alternatively, as shown in FIG. 1B, there is a partial design fault portion b with respect to the opening width 1 h of the opening 1A. When the film forming mask 1 having defects in the opening 1A is used for film formation, the film formation region has an unformed portions c as shown in FIG. 1C. The unformed portions c is formed in accordance with the attachment substance and the design fault portion b, whereby the following problems are caused.
A thin-thickness portion is partially formed in the organic layers interposed between upper and lower electrodes, thereby causing a possibility that a leakage current flows between the upper and lower electrodes so that the emitted light cannot be obtained in a pixel having such a defective film formation region. When a pattern of emission layer is formed, the unformed portion c of the film formation region is formed so that the emission area of the emission layer is reduced and the brightness of the emission is lowered. Additionally, when a layer, which is adjacent to the emission layer, having an electroluminescent is formed on the unformed regions of the film formation region, the color of the emitted light, which is different from predetermined one, is produced so that the chromaticity is changed. This will be described more specifically. When an electron-transport layer made of Alq3 or the like is formed in the unformed portion of red-emitting layer, green emitted-light is produced therefrom, so that the predetermined chromaticity cannot be attained in the unit luminescent areas.
In pattern formation of the electrodes, the electric resistance partially changes due to an unformed portion, so that a predetermined injection current cannot be obtained. In pattern formation of the insulating film or the sealing film, there is the problem in that the insulating or sealing performance is lowered by an unformed portion. The invention is proposed in order to solve these problems.